Previous work from this laboratory has shown significant cardiac contractile dysfunction after a major burn injury despite aggressive fluid resuscitation. Current regimens of inotropic support for the failing heart are often inadequate due to burn-mediated changes in cardiac beta- adrenergic receptor function and altered calcium transport by the cardiac sarcoplasmic reticulum, suggesting that the subcellular basis for postburn cardiac dysfunction is burn-mediated alterations in calcium availability to the myocardial contractile proteins. More recent studies have suggested that neutrophil-derived oxygen free radicals (OFR) damage sarcolemma and subcellular membranes, contributing to postburn cardiac contractile deficits. The goal of this study is to examine the systemic and local cellular and biochemical mechanisms by which burn injury alters cardiac contractile function. This proposal will examine the hypothesis that acute thermal injury initiates systemic ischemia/reperfusion, resulting in intestinal mucosal dysfunction, a loss of gut barrier function, and release of inflammatory mediators which initiate a systemic inflammatory response, which, in concert with local factors lead to profound impairment of myocyte contractile function. To elucidate the local cardiac factors which contribute to postburn cardiac dysfunction, myocytes and neutrophils with be isolated from sham burned, burned animals, as well as from preburn neutrophil depleted animals; myocyte contractile function (velocity of shortening) and intracellular ionic Ca2+ concentrations (measured using the fluorescent calcium indicator, fura-2) will be used to examine the contribution of neutrophils to calcium dyshomeostasis and postburn myocyte contractile function. In addition, we will determine whether one mechanism underlying postburn cardiac contractile dysfunction includes burn-mediated attenuation of cAMP production. In addition, this study will examine the contribution of the neutrophils (and their cytotoxic products) and cytokines on coronary endothelial function and examine the effects of coronary endothelial injury and dysfunction on myocyte contractile function. Finally, this proposal will elucidate the role of neutrophil derived OFR-induced splanchnic vasoconstriction with resultant loss of intestinal barrier function to systemic cytokine release and cardiac contractile dysfunction. These studies will examine the role of the neutrophil as the common denominator initiating injury to intestinal barrier function and to the cardiac myocyte. The long term goal of this proposal is to design treatment strategies based on studies in experimental animals to lessen or prevent cardiac dysfunction after acute thermal injury.